1. Field of the Invention
The present invention relates generally to a fluid-filled cylindrical elastic mount adapted to damp and/or isolate an input vibrational load, based on flows of a fluid contained in a fluid chamber. More particularly, the invention is concerned with such a fluid-filled elastic mount which is simple in construction and can be easily manufactured with high efficiency, and which exhibits excellent vibration isolating characteristics with respect to vibrations applied in the axial direction of the mount, based on the flows of the fluid, while assuring desired vibration damping/isolating characteristics with respect to vibrations applied in radial directions perpendicular to the axial direction indicated above.
2. Discussion of the Prior Art
A cylindrical elastic mount is known for elastically connecting two members in a vibration transmitting system, in a vibration damping or isolating manner. Examples of such a cylindrical elastic mount are disclosed in Publication No. 48-310 of examined Japanese Utility Model Application, and British Patent 1,063,863. The elastic mount as disclosed therein has an inner and an outer sleeve which are disposed in mutually radially spaced-apart relationship with each other, and an elastic body which elastically connects the inner and outer sleeves. This type of elastic mount exhibits predetermined vibration damping and/or isolating characteristics with respect to input vibrations applied in the axial and radial directions of the mount.
In some cases, the cylindrical elastic mount as described above is required to provide different vibration damping or isolating characteristics for input vibrations applied in respective different directions of the mount, e.g., in one axial direction of the mount and two mutually orthogonal diametrical directions perpendicular to the above axial direction. A typical example is an elastic mount which is installed between a suspension member used for a motor vehicle and a body of the vehicle, for connecting the suspension member to the vehicle body. Such a vehicle body mount is required to exhibit a sufficiently low dynamic spring constant with respect to the vibrations applied in the axial direction of the mount or the vertical direction of the vehicle, so as to reduce noises such as road-oriented noises and thereby improve the driving comfort of the vehicle. The body mount is also required to exhibit relatively high hardness or rigidity with respect to the vibrations applied in one of the two orthogonal diametrical directions of the mount, or the transverse direction of the vehicle, so as to prevent postural changes of the vehicle and thereby improve driving stability or maneuverability of the vehicle. Further, the body mount is required to exhibit relatively low hardness or rigidity with respect to the vibrations applied in the other diametrical direction or the front-rear direction of the vehicle, so as to reduce harshness or other vibrations and thereby improve the driving comfort of the vehicle.
In an attempt to meet the above requirements, there is proposed a fluid-filled type elastic assembly or mount, as disclosed in laid-open Publication No. 60-245849 of unexamined Japanese Patent Application, which is assigned to the same assignee as the present application. The disclosed elastic mount has a pair of fluid chambers located between the inner and outer sleeves which are connected by the elastic body, such that the fluid chambers are formed on the axially opposite sides of a partition member which is also provided between the inner and outer sleeves. Such a fluid-filled elastic mount exhibits a relatively low dynamic spring constant with respect to the axially applied vibrations, based on flows of a fluid through an orifice passage which communicates with the fluid chambers. Further, the elastic body for connecting the inner and outer sleeves has a pair of diametrically opposite portions having a relatively large thickness, which portions are opposed to each other in one of the two orthogonal diametrical directions of the mount. This arrangement permits the mount to exhibit relatively high rigidity for the vibrations applied in the above one diametrical direction. In addition, the elastic body has another pair of diametrically opposite portions having a relatively small thickness, which portions are opposed to each other in the other diametrical direction of the mount, whereby the mount is able to exhibit relatively low rigidity for the vibrations applied in the other diametrical direction.
In the disclosed fluid-filled elastic mount, however, the elastic body consists of a first and a second elastic body which connect the inner and outer sleeves with each other at their axially opposite ends, for axially defining an enclosed space between the inner and outer sleeves, and a third elastic body which connects the inner and outer sleeves with each other at their axially intermediate portions, and serves as a partition wall for dividing the enclosed space into two axially aligned fluid chambers. In addition, the elastic mount requires an orifice passage for communicating with the two fluid chambers located on the axially opposite sides of the partition member. Thus, the conventional elastic mount is extremely complicated in construction, and suffers from some problems in terms of assembling procedures and manufacturing cost.